In the manufacture of electrical circuit boards one usually starts from a laminate of copper foil and plastics. The surfaces of the copper foils are coated with a resist in a certain pattern, which resist may be photosensitive, i.e. a photoresist, or by means of silkscreen printing. Subsequently, the exposed copper surfaces are etched in order to leave a conductive pattern on the surface of the plastics board. In circuits which are to be used at high frequencies, for instance for radio frequencies, often the conductors are arranged on one side of the plastics sheet and a ground plane is located on the other side. The ground plane usually is a metal foil without any patterning and covering the entire side on the plastics sheet, where it is located and it will in use be coupled to ground voltage or some reference voltage. In this way an electric signal in the conductor is inductively coupled to the ground plane and this is called microstrip technique. In the similar way the conductor may be enclosed by plastics and ground planes on both the top side and the bottom side and this is stripline technique. In this way circuit functions, including inductances and capacitances, may be accomplished which can be used for instance in frequency filter structures. The characteristics of these circuits are dependent on the plastics material on which the circuit pattern is arranged. Thus the electromagnetic losses, the dimensional tolerances and the dielectric constant of plastic material are determinative of the characteristics of said circuits and the variations of said characteristics.
In conventional circuit board technique often the characteristics of the dielectric must be adjusted in such a way, that the lamination, often with a high pressure, to a copper foil will be possible. Further, the characteristics of the dielectrics must be such, that the dielectric will be relatively easily manipulated in the process for patterning the copper coating.
A large problem is that these requirements highly restrict the choice of possible dielectrics, this implying that material having the best possible electrical characteristics often cannot be selected. Another restricting factor in this context is the requirement that the mechanical dimensions of the conductive pattern should not be influenced too much by temperature changes, since this may cause detrimental stresses on the mounting of components and wire elongation effects in the conductors. Finally, the ambition practically always is that the manufacturing costs should be low and thus, the possibility of achieving low manufacturing costs will generally be restricted due to the restricted possibilities of material selection.